Predicting Anti-Asian Hateful Users on Twitter during COVID-19

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Predicting Anti-Asian Hateful Users on Twitter during COVID-19
Predicting Anti-Asian Hateful Users on Twitter during COVID-19
    Jisun An1 , Haewoon Kwak1 , Claire Seungeun Lee2 , Bogang Jun3 , Yong-Yeol Ahn4
      1
        School of Computing and Information Systems, Singapore Management University
         2
           School of Criminology and Justice Studies, University of Massachusetts Lowell
                           3
                             Department of Economics, Inha University
    4
      School of Informatics, Computing, and Engineering, Indiana University, Bloomington
                {jisunan,hkwak}@smu.edu.sg, claire_lee@uml.edu
                        bogang.jun@inha.ac.kr, yyahn@iu.edu

                      Abstract                              2020) and negativity towards China on Twitter and
                                                            Reddit (Schild et al., 2020). Many Asians have
    We investigate predictors of anti-Asian hate
                                                            expressed an increased level of anxiety and de-
    among Twitter users throughout COVID-19.
    With the rise of xenophobia and polarization            pression due to the recent development of racial
    that has accompanied widespread social me-              animus (Wu et al., 2021). As an attempt to investi-
    dia usage in many nations, online hate has be-          gate online hate towards Asians during COVID-19,
    come a major social issue, attracting many re-          several studies have introduced new datasets and
    searchers. Here, we apply natural language              methods for hate detection towards Asians (Ziems
    processing techniques to characterize social            et al., 2020; Vidgen et al., 2020).
    media users who began to post anti-Asian hate
    messages during COVID-19. We compare                 While most studies focus on the content—e.g.,
    two user groups—those who posted anti-Asian       whether a given text is a hate speech or not, user-
    slurs and those who did not—with respect to a     level analysis—e.g., whether a given user will
    rich set of features measured with data prior to  post hateful content or not—is surprisingly under-
    COVID-19 and show that it is possible to pre-
                                                      explored, although this question can bring useful
    dict who later publicly posted anti-Asian slurs.
    Our analysis of predictive features underlines
                                                      and important insights. First of all, considering
    the potential impact of news media and infor-     the fact that only a handful of users produce the
    mation sources that report on online hate and     vast majority of misinformation (CCDH, 2021) and
    calls for further investigation into the role of  hateful content (§4.2.1), focusing on users may be
    polarized communication networks and news         an efficient way to tackle online hate. For instance,
    media.                                            identifying ‘influential’ users who tend to produce a
                                                      large volume of such content and have the capacity
1 Introduction
                                                      to be the center of the discussion can lead to a better
The novel coronavirus pandemic (COVID-19) pro- intervention than identifying individual instances
vides a unique opportunity to study the develop- of hate speech. Second, understanding the risk
ment of targeted racial animus at an unprecedented    factors for hate speech may also provide an oppor-
scale. Since the first known case of COVID-19         tunity to nudge the users and keep them from being
was reported in Wuhan, China (Mallapaty, 2021), radicalized. This pathway is only possible when
Asians have been a target of online and offline       we examine individual-level risk factors. Finally,
hate. Multiple surveys have shown an increase         because there tends to be much more data avail-
in anti-Asian attitudes among Americans, which        able about individual users than individual tweets
has manifested in xenophobic behaviors, that range    or posts (Qian et al., 2018), we may be able to de-
from not visiting Asian restaurants or changing       velop a more accurate model as well as in-depth
seats to avoiding Asians in public places (Dhanani    insights into the development pathways of online
and Franz, 2020; Croucher et al., 2020; Reny          hate. At the same time, we emphasize that care
and Barreto, 2020) to verbal and physical harass- must be taken when taking user-based approaches
ment (CSHE, 2021; AAPI, 2021).                        because the prediction of future offenses and misbe-
   Online platforms, social media in particular, haviors can potentially lead to algorithmic bias as
have been an exemplification, rather than an excep- shown in the case of recidivism prediction (Angwin
tion, of anti-Asian hate, hosting plenty of hateful   et al., 2016). Thus, our work should be considered
content. Recent work has reported a striking in- an early step towards understanding online hate,
crease of anti-Asian slurs on Twitter (Ziems et al., and we caution that the translation of our results
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               Findings of the Association for Computational Linguistics: EMNLP 2021, pages 4655–4666
                        November 7–11, 2021. ©2021 Association for Computational Linguistics
Predicting Anti-Asian Hateful Users on Twitter during COVID-19
into practice would require much more nuanced            et al., 2017; Waseem and Hovy, 2016; Waseem,
investigation and decision-making.                       2016; Founta et al., 2018), YouTube (Salminen
   In this paper, we tackle online hate towards          et al., 2018), online games (Kwak et al., 2015),
Asians by focusing on users, particularly focus-         and many other online platforms (Zannettou et al.,
ing on the risk indicators of hate towards Asians.       2018), different types of online hate have been in-
We examine users’ language use in their tweets and       vestigated. While leveraging language to detect
information sources that they follow on social me-       hate speech is not new (Schmidt and Wiegand,
dia. As polarization and echo chamber have been          2017), user-level modeling for detecting a future
commonly observed on social media (Garimella             (event-driven) risk of posting hate speeches is rela-
and Weber, 2017; An et al., 2019), it is reasonable      tively unexplored. Among a few, Almerekhi et al.
to expect that users would choose to whom they           (2020) identify linguistic markers that trigger toxi-
listen, often in the way to strengthen their biases.     city in online discussions, Ribeiro et al. (2018) de-
Thus we expect to see signals from the identities of     tect the users who express online hate by checking
the followings of users. Although our retrospective      their profiles or linguistic characteristics, Qian et al.
case-control design does not allow strong causal         (2018) incorporate users’ historical tweets and user
inference (i.e., we cannot discern whether a user is     similarities for hate speech detection, and Lyu et al.
affected by whom they follow or their following is a     (2020) compares hate instigators, targets, and gen-
manifestation of their existing bias), our study may     eral Twitter users by self-presentation, Twitter visi-
shed light on potential mechanisms and pathways          bility, and personality trait. Lyu et al. (2020) char-
towards online hate. Also, while our work focuses        acterize Twitter users who use controversial terms
on online hate, it would provide helpful insights for    associated with COVID-19 (e.g., “Chinese Virus”)
modeling offline hate crimes as well (Relia et al.,      and those who use non-controversial terms (e.g.,
2019).                                                   “Corona Virus”) in terms of demographics, pro-
   Our contributions can be summarized as two-           file features, political following, and geo-locations.
fold. First, we analyze user-level predictors of hate    Unlike previous studies, our work focuses on not
speech towards Asians. We study the impact of            only user features but also on the content posted
both linguistic and information sources, namely (i)      before they start to use Asian slurs, studying the
Content features (social media posts published be-       development of anti-Asian hate attitudes.
fore COVID-19) and (ii) Content-agnostic features           Hate towards Asians during COVID-19 has ap-
(what kind of information a user is exposed to, how      peared through diverse forms. For example, anti-
a user interacts with the platform and other users,      Asian slurs are increasingly used (Schild et al.,
etc). We further study the level of expressed hate.      2020). Also, over 40% of survey respondents in
Second, we will release our dataset (features) and       the U.S. would engage in discriminatory behavior
the code necessary to replicate our results1 .           towards Asians due to fear of COVID-19, lack of
                                                         knowledge about the virus and trust in science, and
2   Related Work                                         more trust in Donald Trump (Dhanani and Franz,
Racial animus has been widely studied from the per-      2020). Reny and Barreto (2020) reported that xeno-
spective of its impact on individuals’ health (Sellers   phobic behavior as well as concerns about the virus
et al., 2003), economic development (Card et al.,        is associated with anti-Asian attitudes.
2008), voting (Stephens-Davidowitz, 2014) and           The context and role of social media in online
social unrest (BBC, 2020b). Understanding how        and offline hate have been argued to be impor-
racial animus is developed is essential to prevent   tant. Croucher et al. (2020) examined a link be-
the risk of further intensifying racial animus and   tween social media use and xenophobia toward
reduce its harm to society.                          Asians. Ziems et al. (2020) demonstrated that they
   Online hater has been studied actively in recent  could identify hate and counterhate tweets with
years. On internet forum (de Gibert et al., 2018),   an AUROC of 0.85. Vidgen et al. (2020) built an
Wikipedia (Wulczyn et al., 2017), News media         annotated corpus for four Asian prejudice-related
comments (Coe et al., 2014), Twitter (Davidson       classes, including criticism without being abusive.
   1
                                                     Their best model achieved a macro-F1 score of
     The data and the corresponding code are avail-
able    at    https://github.com/anjisun221/         0.83, but the only 59.3% of hostility tweets were
Anti-Asian-Slurs                                     correctly identified.
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Predicting Anti-Asian Hateful Users on Twitter during COVID-19
3   Data                                                             Ref     Hate    Low H   High H   Total

We first identify those who express hate towards            Users    2,443   1,899   1,316      583    4,342
                                                            Tweets    250k   8.2M    4.8M     3.4M    10.1M
Asians by collecting data from Twitter in three
steps: 1) compile a list of anti-Asian slurs; 2) col-                  Table 1: Dataset overview
lect tweets with any of the anti-Asian slurs; and
3) identify those who have used anti-Asian slurs
after the pandemic began (we call them hateful            COVID-19 case as the start date of COVID-19.
users) and collect their historical tweets from June
                                                          Refining reference users. As explained above,
8, 2019 to May 8, 2020. Then, as a control set,
                                                          our reference users are randomly selected from a
we randomly sample users who have tweets about
                                                          large collection of COVID-19-related tweets. We
COVID-19 (we call them reference users) and col-
                                                          find that 19 reference users (0.6%) have used anti-
lect their historical tweets during the same period.
                                                          Asian slurs before COVID-19. We exclude those
Anti-Asian slurs. We compile a list of anti-              users for the rest of the study.
Asian slurs by combining 1) Wikipedia’s list of
ethnic slur words (Wikipedia, 2021) that includes         Refining hateful users. Some hateful users have
‘chink,’ ‘chinazi,’ and ‘chicom,’ and 2) a set of         used anti-Asian slurs before COVID-19. Through
COVID-19 specific anti-Asian slurs, such as ‘wu-          manual examination, we notice that most of them
flu’ and ‘kungflu’ (Schild et al., 2020). The full list   are activists in Hong Kong, expressing negativity
of 33 anti-Asian slurs is in Appendix A.                  through slur words targeting China. We exclude
                                                          these users from further analyses.
Hateful users. Using Twint (Poldi, 2021), in                 By contrast, the use of slur words like “wuflu”
May 2020, we collect tweets that contain any of           and “kung flu” began to increase starting from
the anti-Asian slurs from December 31, 2019 to            March 9, 2020, a day when Italy extends emer-
May 1, 2020, resulting in 190,927 tweets posted by        gency measures nationwide (BBC, 2020a), and
120,690 users. We then consider those who 1) live         showed a sharp spike on March 16, 2020, when
in the U.S. and 2) posted at least two tweets with        the former US president Donald Trump referred to
anti-Asian slurs. We use self-declared locations in       COVID-19 as “Chinese Virus” on Twitter (News,
user profiles to infer their state-level location and     2020). Since then, all anti-Asian slurs becomes
exclude users without identified locations. This          widely used. We focus on these users who turned
leaves us with 3,119 hateful users.                       hateful after the COVID-19.
Reference users. As a control set, we construct           Low- vs High-level Hateful users. We further
a set of non-hate users. Using Twitter’s Streaming        divide hateful users into two groups based on the
API, we collect 250M tweets that include COVID-           level of expressed haterism towards Asians. In our
19 related keywords (e.g., “covid” and “coron-            data collection, there are 8,769 tweets that contain
avirus”) from January 13 to April 12, 2020. The           at least one slur word. The average number of
full list of COVID-19 keywords used for this data         tweets with a slur word per user is four (min: 1,
collection can be found in Appendix B. From this          median: 3, max: 126). Thus, we further divide
dataset, we randomly select 3,119 reference users,        users into two groups based on the average tweets
whose location can be detected at state-level and         with slurs: Low-level hateful users with less than
who have not used any anti-Asian slurs.                   or equal to three tweets with anti-Asian slurs and
Historical tweet collections. For the two user            High-level hateful users with at least four tweets
groups, we collect their historical tweets posted for     with anti-Asian slurs.
11 months from June 8, 2019 to May 8, 2020 using
                                                 Bot detection. We further remove ‘bot’ accounts
Twint package (Poldi, 2021). In total, we collect
                                                 to better capture genuine human behaviors. We
18,952,895 tweets where 15.91M (83.94%) tweets
                                                 use Botometer API (Davis et al., 2016), a popu-
of hateful users and 3.04M (16.06%) tweets of
                                                 lar supervised machine learning tool that checks
reference users. We find 15,728 tweets (0.00083%)
                                                 Twitter accounts for possibly automated activity by
containing anti-Asian slurs.
                                                 using features including content, network structure,
Pre- and Post-COVID-19 tweets We use De- and profile. Given a Twitter account, Botometer
cember 31, 2019 when China confirmed the first   API returns a score from 0 to 1, where 1 is the most
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Predicting Anti-Asian Hateful Users on Twitter during COVID-19
likely to be a bot. We use the fifty-percent threshold   from Twitter Decahose data. The unigrams are then
(Botometer score = 0.5), which has proven effec-         ranked by their estimated z-scores.
tive in prior studies (Davis et al., 2016), to remove
potential bot accounts.

Data summary. As a result, our data collec-
tion for further analyses contains 8,201,510 and
2,498,246 tweets posted by 1,899 hateful users and
2,443 reference users, respectively. We also collect
their network information—whom they follow by              (a) (Pre) Hateful users    (b) (Pre) Reference users
using Twitter REST API. Details are in Table 1.

4     Comparative Exploration of Hateful
      and Reference Users
Prior to predicting future hate behaviors of users,
we first conduct a comparative exploration between
                                                           (c) (Post) Hateful users   (d) (Post) Reference users
hateful users and reference users to better under-
stand their discriminating characteristics.
                                                         Figure 1: Over-represented unigrams of Hateful users
                                                         and Reference users for Pre- and Post-COVID-19
4.1     How much and what they write
4.1.1    Twitter Activity                               Figure 1 shows the 100 most over-represented
The first noticeable difference between hateful      unigrams from each corpus. For hateful users be-
users and reference users is their activity level    fore COVID-19 (Figure 1(a)), US politics-related
in terms of the number of written tweets after       words (e.g., obama, biden, clinton, conservative,
COVID-19. On average, both user groups in- and democrat) and international political issue-
creased their activities, and the increase is more   related words (e.g., iran, border, war, and ukraine)
considerable for hateful users. We evaluate the      are presented. Some words indicate that these users
statistical significance by 1,000 bootstrapped sam- are likely to be right-wing: 1) maga (“Make Amer-
ples. The bootstrapped average percent increase      ica Great Again”) is a campaign slogan used in
among hateful users is much higher than reference    American politics popularized by Donald Trump,
users: 90.12 % (±0.419 %, 95% CI) vs. 24.52 %        2) terms like leftists and socialist, and 3) right-wing
(±0.107 %, 95% CI). Furthermore, we observe that     news media, including breitbartnews, gatewaypun-
the increase in activity after COVID-19 is driven    dit, and dailycaller. Another interesting word set
more by those High-level hateful users than Low- contains names: soros (likely George Soros), omar
level ones. The bootstrapped average percent in- (likely Ilhan Omar), schiff (likely Adam Schiff),
crease among High- and Low-level hateful users       and nancy (likely Nancy Pelosi), who opposed
are 118.97 % (±0.977 %, 95% CI) and 77.22 %          Donald Trump. Also, a hashtag ‘#votebluenomat-
(±0.381 %, 95% CI), respectively.                    terwho’ seems to be used by hateful users.
                                                        The reference users’ prominent words before
4.1.2 Representative Words of User Groups            COVID-19 (Figure 1(b)) look more casual than
As an exploratory analysis, we identify the repre- hateful users, which also show the validity of
sentative words of user groups by using the log- our reference sample to some extent. The over-
odds ratio proposed in (Monroe et al., 2008). For    represented words are related to sports and enter-
each group, we aggregate all their pre-COVID-19      tainment (e.g., nba, football, game, and music),
and post-COVID-19 tweets separately, creating the    and K-pop (e.g., bts, nct, and exo), which is one of
four corpora. To remove rare jargon, we elimi- the globally popular topics on Twitter (Kim, 2021).
nate terms that appear less than 10 times. We then   Also, words with positive connotations (e.g., love,
extract all unigrams and compute their log-odds      happy, thank, congrats, and excited, lmao (“laugh-
ratio. As the prior, we compute background word      ing my ass off”)) are appeared. We find some N-
frequency on two separate random Twitter datasets    word expressions from this group, suggesting the
for pre-COVID-19 and post-COVID-19, sampled          presence of more black Twitter users in this group.
                                                  4658
After COVID-19, hateful users seem to actively       To examine what information users are exposed to,
write tweets about COVID-19 (Figure 1(c)), includ-      we opt for analyzing news URLs shared by users.
ing China, Chinese, virus, flu, death, and Wuhan.       In doing so, we use media-level factuality ratings
Words related to infodemic, such as propaganda,         on a 7-point scale (Questionable-Source, Very-Low,
fake, wrong, lying, and truth, are also presented,      Low, Mixed, Mostly-Factual, High, and Very-High)
which is well aligned with a previous report (Cinelli   and bias ratings on a 7-point scale (Extreme-Left,
et al., 2020).                                          Left, Center-Left, Center, Center-Right, Right, and
   Lastly, Figure 1(d) shows reference users’ over-     Extreme-Right) annotated by the Media Bias/Fact
represented words after COVID-19. We do not see         Check (MBFC) (Zandt, 2015).
many changes for this group but note two particular
words: kobe and medicareforall. Kobe (Bryant) is

                                                        # of shared URLs (per user)
                                                                                                     Hateful

                                                                                                                                                             # of shared URLs (per user)
                                                                                      6                                                                                                    10.0                                            Hateful
                                                                                                     Reference                                                                                                                             Reference
an NBA superstar who passed away in January                                           4
                                                                                                                                                                                            7.5

                                                                                                                                                                                            5.0
2020. Since ‘medicareforall’ is one of the key                                        2
                                                                                                                                                                                            2.5
slogans of the Democrats, this suggests that more                                     0                                                                                                     0.0

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left-wing users may be present in the reference

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users.                                                                                                              Media Bias                                                                                    Media Factuality

                                                                                                            (a) Bias                                                                                    (b) Factuality
4.1.3 How their tweets are engaged by others
We examine how actively other users engage in

                                                                                                                                                             # of shared URLs (per user)
                                                        # of shared URLs (per user)
                                                                                                     High-level Hateful                                                                    25                                      High-level Hateful
                                                                                                     Low-level Hateful                                                                                                             Low-level Hateful
                                                                                      15                                                                                                   20
hateful users’ tweets. The average retweet (like)                                     10                                                                                                   15

counts of hateful users is 1.88 (7.88), while that                                    5
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of reference users is 1.47 (7.68). We run a Mann-                                     0                                                                                                     0

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Whitney’s U test to evaluate the difference and
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find a significant effect of group for retweet counts                                                                Media Bias                                                                                 Media Factuality

(U = 6.05, p < 0.001), but not for like counts.                                            (c) Bias, High vs Low                                                             (d) Factuality, High vs Low
Furthermore, high-level hateful users tend to have
higher retweet counts but lower like counts than                                           Figure 2: Shared News Media before COVID-19
low-level users. The average retweet (like) counts
are 2.97 (1.01) and 1.11 (6.29) for high-level and         We compare the average number of shared URLs
low-level hateful users, respectively. The differ-      for each of categories in media bias (Figure 2(a))
ences of retweet and like counts are statistically      and factuality (Figure 2(b)) between hateful and
significant (p < 0.001 and p < 0.05, respectively).     reference users from their pre-COVID-19 tweets.
   Lastly, tweets with anti-Asian slurs tend to be      Across all categories, hateful users share more
more retweeted and liked than other tweets of hate-     news URLs than reference users. While the rep-
ful users. The average retweet (like) counts are 4.52   resentative word analysis hints that hateful users
(10.87) for tweets with anti-Asian slurs and 1.87       are more likely to be right-wing, their shared news
(7.88) for other tweets. We find that the like count    are fairly diversified. While hateful users share
difference is statistically significant (p < 0.001)     URLs from credible news media, they also share
but not the retweet count. The results indicate that    many news URLs from less credible news media.
the tweets posted by hateful users are more likely      When comparing high-level and low-level hateful
to be propagated and thus get exposed to the target     users, active news sharing behavior of hateful users
group. Moreover, it suggests that there may exist       mostly comes from high-level hateful users.
positive feedback for hateful tweets—expressing
hate tends to increase engagement, which in turn        4.2.2                                            Followings
may nudge users to post more hate tweets.              The accounts following is yet another proxy of in-
                                                       formation sources. We examine Twitter accounts
4.2 What They Consume and Share
                                                       that are the most followed by each group. For refer-
4.2.1 Shared News Media                                ence users, the top 5 are ‘BarackObama’, ‘realDon-
News is known to be powerful in shaping people’s       aldTrump’, ‘nytimes’, ‘AOC’, and ‘cnnbrk’, while
opinions and behaviors (McCombs and Valenzuela, those by hateful users are ‘realDonaldTrump’, ‘Re-
2020). A potential bias or factuality of news report- alJamesWoods’, ‘POTUS’, ‘DonaldJTrumpJr’, and
ing thus can influence one’s attitude towards Asians. ‘TuckerCarlson’. In the top 50 Twitter accounts
                                                    4659
followed by the two groups, only 5 are in common,        readability), bias (Recasens et al., 2013; Mukherjee
indicating that the information sources of the two       and Weikum, 2015), and morality (Graham et al.,
groups are distinctive. Among hateful users, the         2009; Lin et al., 2018). These features are known to
overlap between low- and high-level hateful user         be indicative for detecting fake information and the
groups is high—45 of the top 50 are shared.              political bias of news sources. We expect that they
                                                         help to capture aspects of factuality or political
4.3     Summary                                          bias of hateful users’ tweets. For each user, we
In sum, hateful users, as a group, exhibit noticeable    obtain her NELA features by averaging the NELA
differences in comparison with the reference users,      features of her tweets.
including 1) being more active on Twitter during
                                                         Psycholinguistics Features: We extract features
COVID-19, 2) using more words about politics (es-
                                                         that relate to emotional and psychological charac-
pecially right-wing), 3) sharing significantly more
                                                         teristics of users by using Linguistic Inquiry and
URLs of news media, and 4) having distinctive
                                                         Word Count (LIWC) (Pennebaker et al., 2015).
information sources.
   High-level hateful users can be further differen-     Embedding Features: We encode each tweet
tiated from low-level ones by the following fea-         using Sentence BERT (SBERT) (Reimers and
tures: 1) they increased Twitter activity even more      Gurevych, 2019) for the following reasons: 1) the
(about 54% more than low-level hateful users) after      distribution of the number of tweets per user is
COVID-19, 2) their tweets tend to be more shared         highly skewed, and 2) tweet has a sentence-like
and liked, and 3) they share more URLs published         structure and length. Thus, we opt for SBERT
by news media of extreme bias and low factuality.        and average the SBERT representations across the
                                                         sample tweets to obtain a user-level representation.
5     Predicting Hateful Users                           The averaged user-level representation is a 768-
Our comparative exploratory analysis indicates that      dimensional vector.
there exist significant differences between these        Shared News Media: We also consider news
groups, raising an important question: can we pre-       media shared by users as features because they
dict those who turned hateful by only using the          can be a proxy for information sources that users
information available prior to the pandemic? The         consume and propagate. Using seven categories
possibility of such prediction, combined with the        of bias and factuality of news media introduced in
analysis of prominent predictors, may help us un-        §4.2.1.
derstand the pathways into xenophobic haterism
and design potential interventions.                      5.1.2 Content-agnostic features
                                                         We model users based on how they interact with
5.1     Features                                         others and how they portray themselves to their
For each user, we extract 1) content features and 2)     audiences by using their Twitter profiles.
content-agnostic features for training a classifier to   Twitter Statistics: We use basic information ex-
predict the future hate expression towards Asians.       tracted from a Twitter profile, such as 1) whether a
5.1.1    Content Features                                user’s account is verified by Twitter; 2) the number
                                                         of days since the account was created; and 3) four
From the over-represented words in Figure 1, we
                                                         Twitter statistics including the number of followers,
observe that word usage is distinct between the two
                                                         followings, tweets, and favorites.
user groups. We thus extract content features from
the pre-COVID-19 tweets of every user. Since the         Twitter Profile Description: Since most of the
distribution of the number of tweets per user is         Twitter profile description (bio) is short and has
skewed, we sample 198 tweets per user, a median          a sentence-like structure, we encoded the user’s
number of pre-COVID-19 tweets per user, and ex-          profile description using SBERT, like Baly et al.
tract content features from the sampled 198 tweets.      (2020) did for obtaining followers’ representations.
NELA Features: We extract following linguistic         Twitter Following: We consider those who fol-
features by using the News Landscape (NELA) lowed by a given user as features, which capture
toolkit (Horne et al., 2018): text structure (e.g., whom they listen to (information source). First,
POS tags), sentiment, subjectivity, complexity (e.g., we identify the top 50 Twitter accounts followed
                                                    4660
by each user group and obtain their union, which         features generally shows improvements, except for
results in 95 Twitter accounts. Then, for each user,     one case—profile description features yield loss in
we check whether one follows each of them and            performance when added to the following features
create a 95-dimensional vector as the following          (row 7). Twitter statistics and profile description
features.                                                improve the performance when combined with the
                                                         following features, yielding the best performance
5.2   Experimental Setup                                 among content-agnostic features (row 8).
We evaluate (i) content and (ii) content-agnostic           Rows 9-12 show that average embeddings of
features separately and in combinations. We train        tweets by SBERT (row 12) work better than NELA
XGBoost classifier for predicting whether or not a       features (row 10) or LIWC features (row 11). We
user will express hate towards Asians in the future.     note that a combination of shared news media,
Although we could have adopted other models to           NELA, and LIWC features shows improvements
improve the performance, our focus is on under-          (row 19), but they are worse than using SBERT fea-
standing risk factors rather than building the best      tures. While news media features alone do not yield
prediction models. We thus chose XGBoost, which          good performance, it gives a sizable improvement
is highly robust across different data and problems,     by +0.55 macro-F1 points (row 15) when added to
regularly outperforms more sophisticated models.         the SBERT features, which is the best performance
We perform an incremental ablation study by com-         among content features.
bining the best features from (i) and (ii) to achieve       Finally, rows 24 and 26 show the results when
even better results. We split data in 80:20 ratio for    combining content and content-agnostic features.
training and testing. With training data, we train       The best result is achieved using all features (row
and evaluate an XGBoost model using different            26). This combination improves over using in-
features and feature combinations. At each itera-        formation from contents only (row 15) by +2.47
tion of the 5-fold cross-validation, we perform a        macro-F1 points. The result indicates that not
grid search to tune the hyper-parameters of our XG-      only users’ tweets but their information sources
Boost model, which are the maximum tree depth            have strong predictive power to identify those who
and the minimum child weight that controls for           would express hate against Asians after COVID-
complexity and conservativeness, respectively. We        19, demonstrating the advantage of the user-level
use the learning rate of 0.1, gamma of 0.1, and col      approach than tweet-level approach.
tree of 0.8. In the search process, we optimize for
macro-average F1 score, i.e., averaging over the         5.4   T2: High-level Hateful User Prediction
classes, since our dataset is not balanced for both
tasks. Finally, we evaluate the model on the unseen     The second task is to predict whether a user would
testing data. We report both macro F1 score and         turn into high-level hateful users against Asians. Ta-
accuracy and compare our result with the majority       ble 2 (Column 7 & 8) shows the evaluation results.
class baseline.                                         We note that the dataset for this task is imbalanced
                                                        (See Table 1), yielding high accuracy (71.05) for
5.3 T1: Hateful User Prediction                         our baseline, majority class model. Overall, the
Table 2 shows the evaluation results for future hate    performance of this task is not as high as hateful
prediction grouped by feature categories. For each      user prediction, reflecting the difficulty of this task.
category, the upper rows correspond to an individ-         Similar to the result of hateful user prediction,
ual set of features, while the lower ones show their    rows 2-4 suggest that ‘whom they follow’ is more
combinations.                                           important than Twitter statistics or profile descrip-
   Rows 2-4 show that whom they follow (row 4) is       tion. Rows 5-9 suggest that a combination of Twit-
the most useful feature among the content-agnostic      ter statistics and following features (row 6) result
features. As followings determine what kinds of         in the highest performance among content-agnostic
information a user would be exposed to, this result     features. Rows 9-12 indicate that LIWC features
indicates two groups are likely to be exposed to a      (row 11), which capture the psycholinguistic char-
very different set of information at least on Twitter. acteristic of users, are better than embedding and
   Rows 5-8 show the results of the models that         NELA features. Combining shared news media,
combine Twitter statistics, profile description, and    NELA, and LIWC (row 19) shows a slight im-
following features. Combining content-agnostic          provement over the model using LIWC features.
                                                     4661
Hateful User       High-level Hateful User
      Model          #    Features                       Dim.
                                                                    Macro F1 Accuracy     Macro F1 Accuracy
      Baselines      1    Majority class                             36.15      56.62       41.54        71.05
      A. Content     2    Twitter Statistics              6          67.87      68.58       46.88        67.37
      -agnostic      3    Profile Description: SBERT     768         64.60      66.05       46.88        67.37
      features       4    Following                      95          80.04      81.01       51.41        63.95
                     5    Twitter Stat. + Prof.          774         72.52      73.30       49.29        68.68
                     6    Twitter Stat. + Fol.           101         80.63      81.13       58.80        69.21
                     7    Twitter Prof. + Fol.           863         79.22      80.21       50.29        67.11
                     8    Twitter Stat. + Prof. + Fol.   869         80.98      81.70       51.36        67.37
      B. Content     9    Shared News media              14          67.87      71.35       49.82        68.68
      features       10   Tweets: NELA                   85          74.20      74.68       54.44        66.32
                     11   Tweets: LIWC                   73          76.36      76.75       55.06        67.63
                     12   Tweets: SBERT                  768         81.55      81.93       49.89        64.47
                     13   Media + NELA                   99          75.38      76.06       55.98        68.42
                     14   Media + LIWC                   87          78.48      78.83       56.32        68.42
                     15   Media + SBERT                  782         82.10      82.51       48.47        64.21
                     16   NELA + LIWC                    158         77.64      78.02       53.60        66.58
                     17   NELA + SBERT                   853         81.68      82.05       53.23        66.58
                     18   LIWC + SBERT                   841         81.43      81.82       47.43        63.95
                     19   Media + NELA + LIWC            172         78.62      79.17       55.98        68.42
                     20   Media + NELA + SBERT           867         81.95      82.39       50.12        66.84
                     21   Media + LIWC + SBERT           855         81.17      81.59       51.33        66.05
                     22   NELA + LIWC + SBERT            926         81.24      81.70       53.78        67.89
                     23   Tweets: ALL                    940         81.49      81.93       47.08        62.63
      Combinations   24   (Task 1) A+B: rows 8 & 15      1651        84.03      84.58         -            -
                     25   (Task 2) A+B: rows 6 & 19       273          -          -         54.58        66.05
                     26   All features                   1833        84.57      85.04       49.17        66.05

Table 2: Ablation study of the proposed features for hateful user prediction (Task 1) and high-level hateful user
prediction (Task 2). The Dim. column indicates the number of features (dimensions) used for each experiment.

   Comparing the best model of content-agnostic                 gust, gross) (Curtis, 2011). Examining the LIWC
features (row 6) with that of content features (row             based model (row 11), hateful users tend to use
19), unlike the results for hateful users predic-               more ‘they’ than ‘I’ or ‘we’ and use more words
tion, content features perform worse than content-              relating to power, risk, religion, male, wear, non-
agnostic features. In other words, it is hard to distin-        fluencies (uh, rr*) and less leisure and work related
guish high-level hateful users from low-level ones              words. Lastly, linguistic features that predict high-
based on what they write (content). Instead, what               level hateful users are: using more negative words
information they subscribe to (following) has more              and ‘I’ and less all capitalized words, punctuation,
explanatory power for the level of hate expression.             positive and anxiety words, and internet slang.

5.5    Important Linguistic Features                            6    Discussion and Conclusion
We examine the important linguistic features us- We presented a study on predicting users who
 ing SHAP (Lundberg et al., 2020). Examining            would express hate towards Asians during COVID-
 the top 20 most important features of the NELA- 19 by using their language use and information
 based model (row 10), hateful users tend to use        sources before COVID-19. We modeled a user
 more strong negative words and ‘there’ while us- by a rich set of features derived from 1) contents
 ing less punctuation, positive words, and plural       published by the user and 2) content-agnostic di-
 nouns. Two moral dimensions, Care/Harm and             mensions, including their Twitter statistics, profile
 Purity/Degradation, are helpful to identify hateful    description, and followings. For hateful user predic-
 users. Hateful users use more words relating to        tion task, our evaluation results showed that most
‘Harm’ (e.g., war, kill) and ‘Degradation’ (e.g., dis- features have a notable impact on prediction per-
                                                     4662
formance, which are tweets represented by SBERT,         and the set of content with anti-Asian slurs would
followings, LIWC, NELA, shared news media,               not completely overlap, we argue that because of
Twitter statistics, and profile description (in this     the aforementioned reasons, our target population
order). For high-level hateful user prediction, fol-     (those who used slurs instead of those who posted
lowing features turn out to be more important than       “hateful content”) is still a useful operationalization
content features. Moreover, embedding features           of anti-Asian hate. Furthermore, this operational-
are worse than NELA or LIWC features, indicating         ization allows a highly transparent and unambigu-
that linguistic styles and information sources are       ous definition of the population. If we target the
crucial for predicting levels of hate towards Asians.    population with “hate towards Asians,” the oper-
                                                         ationalization would inevitably require adopting
   Our retrospective case-control design enabled us
                                                         methods that are much more difficult to understand
to study the distinctive features of hateful users in
                                                         and evaluate. While the keyword-based method
comparison with reference users. We reveal their
                                                         can result in a skewed dataset due to the oversam-
individual importance and contribution, providing
                                                         pling of certain keywords (e.g., n-word) (Vidgen
interpretable insights. In contrast to previous work
                                                         and Derczynski, 2020), since we collect all tweets
focusing on user features on hate content, our study
                                                         containing Asian slurs to study users, not tweets,
sheds light on potential mechanisms and pathways
                                                         we believe the sampling bias would not be a critical
(risk factors) towards online hate. In particular, our
                                                         issue in our study. Furthermore, we would like to
finding that one feature, following, has a strong
                                                         note that we exclude users who have used Asian
predictive power provides compelling sociologi-
                                                         slurs before COVID-19 to ensure that our data cap-
cal relevance. This finding hints at social factors
                                                         tures users who newly developed anti-Asian atti-
(which communities they belong to) potentially be-
                                                         tudes.
ing dominating factor in the development of racial
                                                            For future work, we plan to address the predic-
hatred, suggesting a strong link between social po-
                                                         tion task by ordinal regression that can inherently
larization and xenophobia and calling for actions
                                                         model the level of hate. We are also interested
of social media companies and our society.
                                                         in characterizing hate towards Asians in other lan-
   There are some limitations to our work. First,        guages. Finally, we want to go beyond an observa-
this work is an observational study. Since we model      tional study and attempt to find a potential causal
information sources based on shared URLs and fol-        relationship between information sources (biased,
lowings, we could not know information sources           less credible information) and online hate.
that are neither shared nor followed by users. Sec-
ond, as our study is based on the US and anti-Asian    Acknowledgements
behavior, further studies would require to gener-
                                                       This research was supported by the Singapore
alize our findings for other countries or for other
                                                       Ministry of Education (MOE) Academic Research
ethnic minorities. Third, our target population is
                                                       Fund (AcRF) Tier 1 grant, the DS Lee Foundation
those who used anti-Asian slurs, and thus, other
                                                       Fellowship awarded by the Singapore Management
forms of anti-Asian hate may not be included in
                                                       University, and the University of Massachusetts
this work. However, we argue that not only that
                                                       Lowell’s COVID-19 Seed Award (Mapping Cy-
the keyword-based method is a widely adopted
                                                       berhate toward Asian Americans in Digital Media
approach for studying anti-Asian attitudes during
                                                       Platforms in the COVID-19 Era, 2020-2022). The
COVID-19 (Lu and Sheng, 2020; Schild et al.,
                                                       funders had no role in study design, data collection
2020; Lyu et al., 2020), but also the population
                                                       and analysis, decision to publish, or preparation of
using Asian slurs itself is of great importance be-
                                                       the manuscript.
cause anti-Asian slurs 1) are unambiguously pe-
jorative (Camp, 2013) and context-independent
                                                       Ethical Considerations
(Hedger2010); 2) had not been commonly used un-
like other racial slurs before the pandemic (Schild    While this work provides important insights on the
et al., 2020); and 3) have not been reclaimed by the   development pathways of online hate, it also brings
Asian American community (Croom, 2018); and            ethical implications by potentially being able to
4) their prevalence has been linked to offline be- reveal who may turn to haters. We note that all
haviors and hate crimes during COVID-19 (Lu and        data collected in this study is publicly available,
Sheng, 2020). Although the set of hateful content      and we did not attempt to use any individual-level
                                                    4663
demographic information in our study. Yet, we              BBC. 2020a. Coronavirus: Italy extends emergency
are able to predict whether an individual turns into         measures nationwide.
hateful after the COVID-19 at F1 = 85.57% with
                                                           BBC. 2020b. George Floyd: ’pandemic of racism’ led
simple machine learning methods based on pub-                to his death, memorial told.
licly available Twitter information. The risk of
such user-based predictive tools for future offenses       Elisabeth Camp. 2013. Slurring perspectives. Analytic
and misbehaviors is often underestimated and can              Philosophy, 54(3):330–349.
potentially lead to algorithmic bias, as shown in          David Card, Alexandre Mas, and Jesse Rothstein. 2008.
the case of recidivism prediction (Angwin et al.,            Tipping and the dynamics of segregation. The Quar-
2016). Thus, we once again emphasize that our                terly Journal of Economics, 123(1):177–218.
results should be considered as a first step for fight-
                                                           CCDH. 2021.     The disinformation dozen: Why
ing online hate and further studies are required for         platforms must act on twelve leading online anti-
translating it for practical use. This work is exempt        vaxxers.
from the requirement for IRB review and approval
(Reference #11649).                                        Matteo Cinelli, Walter Quattrociocchi, Alessandro
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